Large colon volvulus is a common, life-threatening cause of colic in horses. Gastrointestinal neoplasia is rare, especially in young horses, but it may contribute to acute abdominal pain. A 1-year-old Standardbred colt presented with acute colic unresponsive to medical treatment. An exploratory laparotomy identified extensive gastrointestinal pathology, and euthanasia was elected due to a poor prognosis. Necropsy revealed a 360-degree volvulus of the caecum and large colon with adhesions, enterotyphlocolitis, and a well-circumscribed mesenteric mass arising from the small intestine. Histopathology in combination with immunohistochemistry (IHC) confirmed the mass as a soft tissue sarcoma (leiomyosarcoma). This case describes the coexistence of intestinal neoplasia and large colon volvulus in a juvenile horse, emphasising the diagnostic challenges and the potential for neoplasms to precipitate acute colic.